There are a variety of methods of molding articles. These include autoclaves, hydroclaves and compression molding. Particularly for high temperature molding (e.g., polyimide resins) one isostatic molding process has shown great advantage over other methods. This method is described in commonly assigned European Patent Application No. 87630010.4 entitled "Molding Method and Apparatus Using a Solid, Flowable, Polymer Medium" to Kromrey. An article is molded by contacting it with a solid polymer medium, such as an especially low strength unfilled silicone rubber which is solid and able to flow readily. Thermal expansion of the medium or mechanical force is used to create molding pressure and thereby provides a substantially uniform pressure on the article precursor. Various temperature and pressure cycles can be attained; constant high pressures can be maintained on the article precursor during cooldown, optionally aided by flowing of medium to and from a vessel in which the article precursor is being molded. The method is particularly adapted to molding filler or fiber reinforced thermosetting polymer composite articles. However, at extreme temperatures, some pressure transferring material may degrade resulting in an oily residue which can be intrusive.
Although there are a wide variety of molding techniques (e.g., isostatic) there is a continual search for improved methods.